Laser disc players have two possible modes of operation which the industry have heretofore considered to be incompatible or mutually exclusive. In one mode the information is stored and retrieved at constant angular velocity. Exactly one revolution along each track or groove then contains one frame of a television or video picture. This one frame can be read out and displayed as a still by repeatedly scanning the same track or groove for so long as this still picture is desired to be held on the screen. Thus, the same groove is scanned (played back) repeatedly, and there is no progression of the scanning head along to the next groove until the still frame is terminated.
In the second mode, information is stored and retrieved at constant linear velocity along the track (groove) being scanned. In this latter mode, as the scanning head progresses outwardly farther from the axis of rotation of the disc, the RPM of the disc drive progressively decreases so that the linear velocity along the track of the disc portion being scanned at each instant by the readout (playback) head remains constant. In this constant linear velocity mode as the diameter of the track progressively increases, the linear length of the track correspondingly lengthens per revolution. Consequently, more than one picture frame is recorded along the track per revolution, and each successive revolution of the track contains more picture elements than the preceding one. A principal advantage of utilizing the constant linear velocity mode is that the playing time for a disc of given size can be much longer than is possible with constant angular velocity recording in that same size of disc.
Heretofore, the laser disc recording industry has been under the universal belief or state of understanding that it is not possible to record a program at constant angular velocity on a disc and also to incorporate still frames into the program. As a consequence of this present universal belief or state of mind in this industry, any program required to contain still frames is recorded entirely at constant angular velocity on the whole disc, which is wasteful of overall playing time. In other words, the playing time of the constant angular velocity recorded disc is relatively brief. Conversely, in this laser disc industry it is current practice that, if a program can be contrived to be devoid of still frames, then the program is recorded on the disc at constant linear velocity in order to utilize the available area on the laser disc more efficiently for achieving as long a playing time as possible with the disc.